Important Flavor Compounds Research Articles

Screening of a Saccharomyces cerevisiae Strain with High 3-Methylthio-1-Propanol Yield and Optimization of Its Fermentation Conditions.

3-Methylthio-1-propanol (3-Met) is an important flavor compound in various alcoholic beverages such as Baijiu and Huangjiu. To maintain the content of 3-Met in these alcoholic beverages, it is necessary to screen a micro-organism with high yield of 3-Met from the brewing environment. In this study, the ability of yeast strains from the Baijiu brewing to produce 3-Met was analyzed, aiming to obtain yeast with high-yield 3-Met, and its fermentation conditions were optimized. Firstly, 39 yeast strains were screened using 3-Met conversion medium. The results showed that the majority of the strains from Baijiu brewing sources could produce 3-Met, and nearly half of the strains produced more than 0.5 g/L of 3-Met. Among these, yeast F10404, Y03401, and Y8#01, produced more than 1.0 g/L of 3-Met, with yeast Y03401 producing the highest amount at 1.30 g/L. Through morphological observation, physiological and biochemical analysis, and molecular biological identification, it was confirmed that yeast Y03401 was a Saccharomyces cerevisiae. Subsequently, the optimal fermentation conditions for 3-Met production by this yeast were obtained through single-factor designs, Plackett-Burman test, steepest ascent path design and response surface methodology. When the glucose concentration was 60 g/L, yeast extract concentration was 0.8 g/L, L-methionine concentration was 3.8 g/L, initial pH was 4, incubation time was 63 h, inoculum size was 1.6%, shaking speed was 150 rpm, loading volume was 50 mL/250 mL, and temperature was 26 °C, the content of 3-Met produced by S. cerevisiae Y03401 reached a high level of 3.66 g/L. It was also noteworthy that, in contrast to other study findings, this yeast was able to create substantial amounts of 3-Met even in the absence of L-methionine precursor. Based on the clear genome of S. cerevisiae and its characteristics in 3-Met production, S. cerevisiae Y03401 had broad prospects for application in alcoholic beverages such as Baijiu.

Screening of a High Ethanol-Producing Saccharomyces cerevisiae Strain and Its Effects on the Dynamics of the Microbial Community and Flavor During Baijiu Solid-State Fermentation

Saccharomyces cerevisiae can metabolize sugars to produce ethanol and secondary metabolites that contribute to the complex flavor profile of Baijiu, a traditional Chinese distilled beverage. The yeasts that contribute to Baijiu fermentation are mostly adventitious strains that show low ethanol production and stress resistance, which results in lower Baijiu yields and quality. Here, we screened S. cerevisiae strains for ethanol production and stress resistance. The best selected strain, SW4, produced a final ethanol titer of 148.1 g/L, which was 113.8% higher than the initial 69.6 g/L. Additionally, the solid-state fermentation of Baijiu with the addition of S. cerevisiae SW4 (QH) resulted in a significant increase in the relative abundance of Pediococcus and Saccharomyces at days 0–14 compared to the control (KB), which may be the main reason for the alteration of Baijiu flavor. Analysis of flavor compounds revealed that QH increased the concentration of alcohols by 44.82% relative to KB after 7 days of fermentation, as well as increasing the concentration of alcohols and esters by 13.06% and 7.11% after 28 days of fermentation. Measurement of 15 differential flavor compounds revealed that 8 were positively correlated with Saccharomyces (p ≤ 0.05), all of which are important flavor compounds contributing to the quality to Baijiu. The Baijiu yield of QH was 25.18%, which was 11.47% higher than that of KB. Overall, this study confirms the positive effects of exogenously added S. cerevisiae on the microbial community structure and flavor of Baijiu at different stages of solid-state fermentation, providing novel opportunities for improving the yield and quality of this important traditional beverage.

Comparison of four drying methods in terms of the drying efficiency and physicochemical properties of chicken meat

In this study, four drying methods, including hot air drying (HAD), catalytic infrared drying (CIRD), electric infrared drying (EIRD), and electric oven drying (EOD), are used to prepare dried chicken breast. The study systematically compares the drying efficiencies of the different methods and their effects on physico-chemical properties, pet food applications, energy consumption, and costs. The results show that CIRD and EOD resulted in a better color of the final product, while the EIRD treatment resulted in the highest degree of denaturation of the chicken breast jerky proteins. In terms of chemical properties, the higher malondialdehyde content of CIRD and EIRD (2.77±0.18 mg/kg, 2.63±0.07 mg/kg) indicated higher fat oxidation in IR-treated chicken meat, which is also associated with an increase in the content of free fatty acids. This paper also found that arachidonic, linolenic, and oleic acids are positively correlated with the content of important flavor compounds in the jerky. For pet food applications, it was found that pets prefer CIRD and EIRD products, and energy and cost measurements also indicate that CIRD (4258.74 kJ/kg, 0.94 yuan/kg) is more energy and cost-efficient than other drying methods. The results show that CIRD (4258.74 kJ/kg, 0.94 yuan/kg) is a more energy-efficient and less costly drying method.

Improved biocatalytic activity of steapsin lipase in supercritical carbon dioxide medium for the synthesis of benzyl butyrate: A commercially important flavour compound

Enzymatic synthesis of flavours, fragrances and food additives compounds have great demand and market value. Benzyl butyrate is commercially important flavour and food additive compound having global use around 100 metric tons/year and widely used in various industrial sectors. However, industrial synthesis of food additive benzyl butyrate is carried out by conventional chemical process which demands for the green biobased sustainable synthetic process. The present work reports steapsin catalyzed synthesis of benzyl butyrate for the first time in supercritical carbon dioxide (Sc-CO2) reaction medium. All reaction variables are optimized in details to obtain competent conversion of 99% in Sc-CO2 reaction medium. The developed steapsin catalyzed synthesis in Sc-CO2 medium offered almost four-fold higher conversion to benzyl butyrate than organic (conventional) solvent. The steapsin biocatalyst was effectually recycled up to five reaction cycles in Sc-CO2 medium. Moreover, the developed steapsin catalyzed protocol in Sc-CO2 medium was extended to synthesize different TEN industrially significant flavour fragrance compounds that offers 99% conversion and three to five-folds higher conversion than organic (conventional) medium. Thus, the present steapsin catalyzed protocol offered improved synthesis of various commercially significant flavour compounds in Sc-CO2. medium.

Metabolomic comparison of meat quality and metabolites of geese breast muscle at different ages.

The purpose of this study was to distinguish the effect of age on the meat quality and chemical composition of Yangzhou goose breast meat. Nontargeted metabolomics analysis (UHPLC-MS/MS) was used to distinguish the metabolic composition of goose meat at different ages, and Pearson's correlations between differential metabolites and key meat parameters were assessed. Compared with goslings, adult geese had lighter, redder and chewier meat (p<0.05). Metabolite analysis revealed significant differences in nucleosides, organic acids, amino acids and sugars. Levels of IMP, xanthosine, pretyrosine and l-threonine were significantly higher in older meat (p<0.05) and positively correlated with meat freshness indicators. However, pyruvic acid, l-cysteine and glucose 6-phosphate were up-regulated in gosling meat (p<0.05), which were important flavor compounds. These results facilitate the further investigation of changes in goose meat composition and provide biomarkers for determining goose meat quality at different ages.

Enhancing biosynthesis efficiency of 2,5-dimethylpyrazine by overexpressing l-threonine dehydrogenase and NADH oxidase in Escherichia coli

2,5-Dimethylpyrazine (2,5-DMP) is a building block for the pharmaceutical intermediate 5-methylpyrazine-2-carboxylic acid, and is also an important flavor compound in food. The chemical synthesis method has the disadvantages of poor selectivity, difficult to separate and purify the product, so it is not suitable for large-scale industrial production. In order to solve the above drawbacks and achieve high efficiency green production of 2,5-DMP, the l-threonine metabolic pathway in Escherichia coli (E. coli) was reconfigured by overexpressing l-threonine dehydrogenase (L-TDH) from E. coli and NADH oxidase (NOX) from Enterococcus faecium with the help of pACYCDuet-1 expression system. The EcTDH and EfNOX activities of the recombinant E. coli BL21(DE3)/pACYCDuet-1-Ectdh-Efnox was 23.55 and 2.83 IU/mL, respectively. And it can convert l-threonine to obtain 2,5-DMP with a yield of 2009.31 mg/L. Therefore, these researchs established solid practice foundation for future large-scale bioconversion of l-threonine to 2,5-DMP.

Temporal Accumulation of Geosmin, Oxalic Acid, and Total Dissolved Solids in Table Beet

Consumers perceive flavor as a critically important attribute of vegetable crops. Gas chromatography-mass spectrometry (GC-MS), spectrophotometry, and refractometry of tissue samples collected during multiple years from table beet (Beta vulgaris) at various stages of maturity were performed to characterize the endogenous production of geosmin, oxalic acid, and total dissolved solids within the root. The geosmin concentration was primarily influenced by the cultivar and peaked early during the growing season, with root concentrations at 6 weeks after planting that were 312% higher, on average, than those found in harvest stage roots at 15 weeks after planting. The highest average concentration of geosmin in harvest stage roots was detected in tissue from the cultivar Bull’s Blood (16.08 μg⋅kg−1). The oxalic acid concentration showed a strong cultivar influence and statistically significant variability across the growing season. Hybrid beet cultivar Boro had the lowest soluble oxalic acid concentration (95.73 mg⋅100 g−1 fresh tissue) at all locations and during all years. The oxalic acid concentration peaked 12 weeks after planting, and it was lower at the postharvest sampling date 18 weeks after planting. Total dissolved solids (TDS) concentrations were strongly influenced by year and growing environment and displayed crossover interactions for environment × week. TDS measurements had a moderate negative correlation with root mass. ‘Chioggia Guardsmark’ consistently had the highest TDS during all years and at all locations at 12.01 °Brix. The TDS varied significantly according to time, and diurnal sampling revealed fluctuations as large as 4 °Brix over the course of a 12-hour period. The TDS concentrations increased throughout the growing season, although the rate at which they increased changed according to plant age. The results from this study suggest that interactions between cultivar, time, and environment are important determinants of oxalic acid and TDS concentrations, but they have less influence on geosmin. This information may influence the methods that plant breeders use to collect phenotypic data of important flavor compounds in beets.

Dynamic changes of microbial community structure and flavor compounds formation during Qingzhi compound-flavor Baijiu fermentation

A Qingzhi compound-flavor Baijiu (QZCF Baijiu) was developed and the physiochemical factors and microbial community structure in Jiupei (fermented grains) during Baijiu fermentation were revealed. Physiochemical factors of ethanol, moisture and acidity significantly increased in the fermentation, while starch and reducing sugar decreased. The results of high-throughput sequencing showed that Weissella, Pediococcus, Bacillus, Pantoea, Streptococcus, Sphingobacterium, Saccharomyces, Rhizopus, Issatchenkia and Wickerhamomyces were the dominant microorganisms in Jiupei. Moreover, correlation analysis between the physicochemical factors, the dominant microorganisms and the important flavor compounds in QZCF Baijiu production highlighted that the changes of physiochemical factors would lead to the corresponding changes of core microbiota and important flavor substances. Physiochemical factors of starch, reducing sugar and temperature could significantly affect the microbial community structure at the early stage of fermentation, while the influences of ethanol content and acidity became greater at the later stage, resulting in the differences of flavor compounds in Jiupei. Therefore, the growth and metabolism of microbial communities could be regulated by purposefully adjusting the physiochemical factors, thereby improving the flavor and quality of Baijiu. This work enriched the flavor types of Baijiu and provided a reference for the Baijiu-making industries to manage their production process.

Vanilla beyond Vanilla planifolia and Vanilla × tahitensis: Taxonomy and Historical Notes, Reproductive Biology, and Metabolites.

Vanilla is a worldwide cherished condiment, and its volatile market is associated with the so-called "vanilla crisis". Even though only two species (Vanilla planifolia and V. × tahitensis) are cultivated on a large scale for commercial purposes, the Vanilla genus is comprised of 140 species. The present review article discusses the facets of this crisis, and vanilla crop wild relatives (WRs) are showcased as alternatives to overcome them. Historical, taxonomic, and reproductive biology aspects of the group were covered. Emphasis was given to the metabolic characterization of the vanilla crop WRs, highlighting their main chemical classes and the potential flavor descriptors. Many of these species can produce important flavor compounds such as vanillin, vanillic acid, and acetovanillone, among others. Overall, this review compiles valuable information that can help unravel new chapters of the history of this treasured product by evidencing the biotechnological potential of vanilla crop WRs.

Using transcriptomics to reveal the molecular mechanism of higher alcohol metabolism in Saccharomyces cerevisiae

High alcohols are important flavor compounds in alcoholic beverages, but high concentration of high alcohols is harmful to human health. Higher alcohol synthesis pathways in brewing microorganisms have been investigated, but the interactions between key genes remain to be explored, especially in industrial strains of Saccharomyces cerevisiae. The PDC1 gene was considered to be the main encoding gene of α-keto acid decarboxylase, and its deletion resulted in a 92.23% increase in isobutanol production and a 14.89% decrease in isoamyl alcohol production. Transcriptome sequencing was used to explore the effects of PDC1 gene deletion on global gene transcription levels, and deletion strategies were utilized to verify the effects of differential genes on higher alcohol production. Deletion of differential gene HMLALPHA2 increased isobutanol production by 26.23%, and decreased isoamyl alcohol and 2-phenylethanol production by 30.31% and 22.35%, respectively. The THI2, THI4, THI20 genes were proved to be related to n-propanol synthesis. In addition, HMRA2 and SIR3 genes were found to influence isoamyl alcohol synthesis pathways, and their deletion increased isoamyl alcohol production by 25.18% and 21.76%. Our discovery of new target genes is useful for elucidating the molecular mechanisms of higher alcohols and the construction of novel low-producing higher alcohol strains.

Development of a Rapid and Sensitive Fluorescence Sensing Method for the Detection of Acetaldehyde in Alcoholic Beverages.

Acetaldehyde is regarded as an important flavor compound in alcoholic beverages. With the advantages of rapidity, low cost and high sensitivity, fluorescent probe could be used as a new tool for the detection of acetaldehyde. Here, an effective fluorescence sensing method based on fluorescent probe N1 (FPN1) was established in this study. The function of FPN1 relies on the nucleophile substitution reaction and photoinduced electron transfer (PET), resulting in a fluorescence increase. Remarkably, the pretreatment background removal method (BRM) was successfully applied for removal of the interference of pyruvate and acetal. The linearity range (LR), limit of detection (LOD) and recovery of the fluorescence sensing method with BRM were 0.0053-200 mg/L, 0.0016 mg/L and 94.02-108.12%, respectively, which showed a broader detection range and better performance on sensitivity compared with the traditional quantitation using gas chromatography (GC). Furthermore, successful application of the method in real samples indicated the advantages of low-cost and rapidity for small-scale detection while assuring the accuracy, which provides a new strategy for the detection of acetaldehyde concentration in alcoholic beverages.

Effects of modernized fermentation on the microbial community succession and ethyl lactate metabolism in Chinese baijiu fermentation

Modernized mechanization and intelligent transformation are the trends of Chinese baijiu industry development. However, these changes affect the operational environment, which lead to the decreased metabolism of esters during baijiu fermentation, especially for ethyl lactate. Ethyl lactate is an important flavor compound in most types of baijiu, which is mainly produced by esterification of lactic acid and ethanol. However, considerably less is known about the dynamic microbial succession related to ethyl lactate metabolism during the modernized baijiu fermentation process. In this study, we investigated the lactic acid bacteria, yeast and mold community succession and ethyl lactate metabolism during baijiu fermentation. Results showed that fermentation mode had a significant effect on lactic acid and ethyl lactate metabolism (p < 0.001). Specifically, the accumulation of lactic acid in modernized process was 50% lower than that in traditional process (23.22 ± 7.41 g/kg versus 33.92 ± 2.32 g/kg fermented grains). The accumulation of ethyl lactate in the modernized baijiu fermentation process (9.46 ± 1.78 g/kg fermented grains) was significantly lower than that in traditional baijiu fermentation process (37.10 ± 5.86 g/kg fermented grains). Moreover, Illumina Miseq sequencing showed 11 lactic acid bacteria OTUs, 6 yeast OTUs and 4 mold OTUs were abundant during fermentation. Compared with traditional baijiu fermentation process, modernized process led to more Lactobacillus and Candida, but less Pichia, Aspergillus, Rhizomucor and Rhizopus during fermentation. Based on the redundancy analysis and correlation network analysis, our study showed the metabolism of ethyl lactate mainly related to the activities of Pichia, Aspergillus, Rhizomucor and Rhizopus, especially for Rhizomucor and Rhizopus. This study revealed that the regulation of Pichia, Aspergillus, Rhizomucor Rhizopus and Candida might be an effective orientation for adjusting the metabolism of ethyl lactate during modernized baijiu fermentation.

Exploring the volatile profile of whiskey samples using solid-phase microextraction Arrow and comprehensive two-dimensional gas chromatography-mass spectrometry

We present a novel sample preparation method for the extraction and preconcentration of volatile organic compounds from whiskey samples prior to their determination by comprehensive two-dimensional gas chromatography (GC × GC) coupled to mass spectrometry (MS). Sample preparation of the volatile compounds, important for the organoleptic characteristics of different whiskeys and their acceptance and liking by the consumers, is based on the use of the solid-phase microextraction (SPME) Arrow. After optimization, the proposed method was compared with conventional SPME regarding the analysis of different types of whiskey (i.e., Irish whiskey, single malt Scotch whiskey and blended Scotch whiskey) and was shown to exhibit an up to a factor of six higher sensitivity and better repeatability by a factor of up to five, depending on the compound class. A total of 167 volatile organic compounds, including terpenes, alcohols, esters, carboxylic acids, ketones, were tentatively-identified using the SPME Arrow technique, while a significantly lower number of compounds (126) were determined by means of conventional SPME. SPME Arrow combined with GC × GC-MS was demonstrated to be a powerful analytical tool for the exploration of the volatile profile of complex samples, allowing to identify differences in important flavour compounds for the three different types of whiskey investigated.

Py-GC–MS Investigation of Pyrolysis Behaviors and Decomposition Products of α- and β-2,7,11-cembratriene-4,6-diols

Py-GC–MS Investigation of Pyrolysis Behaviors and Decomposition Products of α- and β-2,7,11-cembratriene-4,6-diols May 1, 2022 Shen Huang, Chen Yang, Ning Ma, Lifeng Zhou, Chunxiao Jia, Tao Wei, Duobin Mao LCGC North America, May 2022, Volume 40, Issue 5 Pages: 223–228 To study the thermal stability of cembratriene, α- and β-2, 7, 11-cembratriene-4, 6-diols (α- and β-CBT) were isolated from tobacco leaves. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were used to evaluate the cleavage differences between the two compounds. The TGA results showed the peak temperatures (Tp) were 263.3 °C and 254.1 °C with the largest weight loss rate; the significant weight losses were 90.96% and 99.45%. Pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) was employed for the pyrolysis products at different temperatures (300, 600, and 900 °C) under either N2 or an O2:N2 (10%:90%) mixture. The results showed that the major pyrolysates from α- and β-CBT were simple hydrocarbons, such as toluene, 1, 4-pentadiene, and p-xylene, as well as several important flavor compounds, such as 2-methylfuran, benzaldehyde, and 4-methylbenzaldehyde. More pyrolysis products were obtained at higher temperatures, and almost all of the harmful aromatic ingredients were produced at 900 °C. Importantly, solanone, a significant flavor component, was only obtained from the pyrolysis of α-CBT under 10% O2 in N2 at both 600 and 900 °C. The number of the pyrolysates changed with the change in pyrolysis temperature and the presence of oxygen. The study of the thermal behavior and pyrolysis products of these terpenoids could possibly suggest flavor precursors that could be used to provide specific flavors.

Mesopic fermentation contributes more to the formation of important flavor compounds and increased growth of Lactobacillus casei Zhang than does high temperature during milk fermentation and storage

Probiotic fermented milk is more and more popular due to their positive health associated properties. However, fermentation temperature and other process conditions may affect the growth and metabolism of probiotic strains, thereby affecting quality of the final products. In this study, the growth behaviors and metabolomic profiles of yogurts induced by Lactobacillus casei Zhang at fermentation termination (FT) and d 10 of storage (S10d) under different fermentation temperatures at 37°C (low) and 42°C (high) were analyzed and compared using liquid chromatography-mass spectrometry (MS)- and gas chromatography-MS-based metabolomics approaches. At 37°C, the growth of L. casei Zhang at FT and S10d was significantly increased, and the potential relationship between riboflavin, starch, and sucrose metabolism and growth of L. casei Zhang may be mutually promoting. Fermentation temperature (37°C and 42°C) affected volatile and nonvolatile metabolomic profiles and pathways. The levels of acetaldehyde, 2,3-butanedione, acetoin, butyric acid, decanoic acid, hexanoic acid, and octanoic acid were significantly higher at 37°C than at 42°C at FT and S10d. This indicates that the low temperature (37°C) most likely contributes more to the formation of important flavor compounds during the fermentation process and production of short-chain fatty acids during storage.

The effect of flash vacuum cooling on the flavor of ultrapasteurized milk

Ultrapasteurization (UP) extends the shelf life of milk. Direct steam injection (DSI) is commonly used for UP because milk is quickly heated and cooled. During this process, steam is directly injected into milk and removed by a vacuum cooler. Consumers do not prefer the flavor of DSI-UP milk compared with traditional high temperature short time (HTST) milk due to the higher cooked and eggy flavors of DSI-UP milk. The objective of this research was to characterize the effect of the vacuum cooler on the flavor of DSI-UP milk. Raw skim milk was pasteurized at 140°C for 2.3 s by DSI and homogenized at 20.7 MPa. By using a liquid sample port, steam-infused pasteurized milk was sampled after heating but before reaching the vacuum chamber. A septum was installed in the vacuum chamber to allow sampling of the removed volatiles by solid-phase microextraction (SPME) fiber followed by gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) combined with a sulfur-selective flame photometric detector. Steam-infused milk and vacuum-cooled milk diluted to the same solids contents were evaluated by descriptive sensory analysis and volatile compound analysis. The entire experiment was replicated 3 times. Milks cooled by the vacuum cooler were lower in sweet aromatic, sulfur/eggy, and cooked flavors than milk sampled before the vacuum cooler. Volatile compounds removed by the vacuum cooler included the sweet aromatic flavor contributors furaneol, maltol, furfural, sotolon, 2-heptanone, γ-dodecalactone, γ-decalactone, and δ-decalactone, as well as the cooked and sulfur/eggy contributors hydrogen sulfide and dimethyl sulfide. The vacuum cooler applied during DSI-UP of milk is effective at removing steam and cooling UP milk, but this process may also remove important flavor compounds from fluid milk.

Vanilla flavor: Species from the Atlantic forest as natural alternatives

The volatility of the vanilla market calls attention to the so-called vanilla crisis. There is a growing worldwide demand for natural vanilla with a concomitant reduction in global supply. However, commercial crops are threatened with extinction due to the lack of gene pool variability, susceptibility to climate change and pandemic diseases. Therefore, there is an urgent need to identify new Vanilla spp. as alternative sources vanilla. Therefore, using undirected LC-MS/MS metabolic profiling and chemometrics, the present study demonstrates the great bioeconomic potential of two Atlantic Forest species - V. bahiana and V. chamissonis - by annotation of important flavor compounds associated with the commercial species and reveals distinct flavor descriptors associated with both wild species. Such similarities and dissimilarities are crucial to the ongoing quest to Vanilla gene pool improvement. Compounds remarkably and frequently associated with vanilla flavor were annotated or identified in this study such as vanillin and p-hydroxybenzaldehyde.

Profiling the influence of physicochemical parameters on the microbial community and flavor substances of zaopei

Strong-flavor baijiu is a traditional distilled alcoholic beverage with a long history in China. The fermented grains play a pivotal role in the production of baijiu. The purpose of this study was to evaluate and compare the microbiota and flavor substances present in fermented zaopei (ZP) from pits of different ages. High-throughput sequencing, headspace solid-phase microextraction gas chromatography-mass spectrometry, principal component analysis, community composition analysis, and redundancy analysis were used to analyze and evaluate the impact of environmental factors on microbial communities and flavor substances. Six genera of bacteria (e.g., Caproiciproducens, Syntrophaceticus, Sedimentibacter, Hydrogenispora, Pelotomaculum and Bacillus) and seven genera of fungi (Cladosporium, Debaryomyces, Dipodascus, Auxarthron, Cephalotrichum, unclassified Stachybotryaceae, unclassified Microascaceae and Cephalotrichum) notably affected the production of hexanoic acid (an important flavor compound). Moisture and alcohol content also had considerable effects on the production of the flavor compounds such as ethyl lactate, hexanoic acid, and ethyl hexanoate. The profiles of volatile compounds present in ZP were different between the aged and new pits; these profiles were mainly reflected in the concentration and types of alcohols, aldehydes, esters, and aromatic compounds. This paper provides a comprehensive overview of the physicochemical parameters, flavor substances, and microbial population distribution of ZP. Characterization of various ZP samples help to elucidate the fermentation mechanisms and offer a theoretical reference to control and enhance the quality of Baijiu. © 2021 Society of Chemical Industry.

The revenge of Zygosaccharomyces yeasts in food biotechnology and applied microbiology.

Non-conventional yeasts refer to a huge and still poorly explored group of species alternative to the well-known model organism Saccharomyces cerevisiae. Among them, Zygosaccharomyces rouxii and the sister species Zygosaccharomyces bailii are infamous for spoiling food and beverages even in presence of several food preservatives. On the other hand, their capability to cope with a wide range of process conditions makes these yeasts very attractive factories (the so-called "ZygoFactories") for bio-converting substrates poorly permissive for the growth of other species. In balsamic vinegar Z. rouxii is the main yeast responsible for converting highly concentrated sugars into ethanol, with a preference for fructose over glucose (a trait called fructophily). Z. rouxii has also attracted much attention for the ability to release important flavor compounds, such as fusel alcohols and the derivatives of 4-hydroxyfuranone, which markedly contribute to fragrant and smoky aroma in soy sauce. While Z. rouxii was successfully proposed in brewing for producing low ethanol beer, Z. bailii is promising for lactic acid and bioethanol production. Recently, several research efforts exploited omics tools to pinpoint the genetic bases of distinctive traits in "ZygoFactories", like fructophily, tolerance to high concentrations of sugars, lactic acid and salt. Here, I provided an overview of Zygosaccharomyces industrially relevant phenotypes and summarized the most recent findings in disclosing their genetic bases. I suggest that the increasing number of genomes available for Z. rouxii and other Zygosaccharomyces relatives, combined with recently developed genetic engineering toolkits, will boost the applications of these yeasts in biotechnology and applied microbiology.

Comparison of the microbial community and flavor compounds in fermented mandarin fish (Siniperca chuatsi): Three typical types of Chinese fermented mandarin fish products

Fermented mandarin fish have been receiving attention from consumers due to their nutritional value and specific flavor. Microbial diversity in fermented mandarin fish has an important impact on their flavor and quality. However, little is known about the microbiome and the differences among different products. In this study, the bacterial profiles and flavor compounds in three typical fermented mandarin fish products were investigated and compared, and a correlation network was used to explore the potential relationship between microorganisms and flavor. Bacterial community analysis demonstrated clear differences in microbiota among the HF-, MF-, and OF-fermented mandarin fish products. Psychrilyobacter, Fusobacterium, and Vibrio were the most dominant in the HF-, MF-, and OF-fermented products, respectively. In addition, 14, 12, and 4 flavor substances (relative odor activity value, ROAV ≥ 1) were detected in the muscles from the central dorsal and ventral sides of the three samples, respectively. Several bacteria correlated with the production of important flavor compounds, and three genera (Arcobacter, Psychrilyobacter, and Shewanella) were the primary microorganisms contributing to more than six characteristic flavor compounds in fermented mandarin fish products. Therefore, the study’s systematic method allows identificating important microbes and characteristic volatile flavor compounds in fermented mandarin fish and provides new insights into the relationship between microorganisms and flavor.